How to Grow 1 Gram of Cannabis per Watt of Light?

One gram per watt of Cannabis is the indoor harvest you acquire from a particular grow light wattage. To make this possible, you have to regulate the growing environment, choose appropriate growing lights, select high-yielding strains, and train your Cannabis plants. You may also consider adding Carbon Dioxide for Cannabis to grow faster and have enhanced quality of yields. 

How to Grow 1 Gram of Cannabis per Watt of Light?

What is 1 gram per watt of Cannabis?

One gram per watt of Cannabis refers to the harvest you get from a specific wattage of grow light used by indoor growers. Achieving one gram per watt of Cannabis is already impressive. One gram per watt is the optimum, or the "upper limit" of harvest from indoor grows. Though, it is still possible to go beyond this. You can even produce 2 grams per watt with the help of a quality LED grow light accompanied by the right skills and a good growing environment setup.

How to calculate grams per watt?

Knowing how to calculate the harvest will track your progress as a grower. At the same time, it will serve as your basis to evaluate efficiencies and adjust to going beyond your harvest. Thus, it would be best to learn how to calculate one gram per watt of Cannabis.

The formula of Yield per Watt of Light is given by the Total Dried Product ÷ Total Lamp Wattage = Yield per Watt of Light


(a) If you use 500 watts of grow light, then you harvested 500 grams of bud, you have

500 grams ÷ 500 watts = 1 gram/watt

(b) Using the same 500 watts, you harvested 250 grams of buds, then you have

250 grams ÷ 500 watts = 0.5 gram/watt

(c) During this time, your total yield is 1000 grams of bud from using 500 watts of grow light, so you have

1000 grams ÷ 500 = 2 grams/watt

How to produce 1 gram of cannabis per watt of light?

Achieving 1 gram of Cannabis per watt of light requires time and effort. It does not happen overnight, but it is a work in progress. The following tips are simple, but they will surely help you make a massive difference with your harvest if you keep your mind to them. 

Regulating growing environment

Avoid extreme temperatures, for it can slow down the growth of your Cannabis and other plant problems. You have to regulate the temperature of your growing environment between 65° to 85° Fahrenheit (18° to 30° Celsius) during the whole growing. Specifically, keep it around 75° to 80° Fahrenheit (24° to 27° Celsius) during the day and a few degrees cooler at night.

In addition, keep 50% relative humidity throughout the growing. Young seedlings and clones need a few humidity increases, but they can still thrive at 50%. Also, you need to ensure proper air circulation to avoid hot air going around your growing space. Your crops grow ideally in a breezy environment with fresh air to grow healthier and fast.

Selecting Grow Lights

The easiest way to achieve 1g/watt of light is by using LED lights as they convert most of the electrical energy into light. Other growing lights like HPS and LEC produce a lot of heat and are thus very inefficient from an electricity standpoint.
If you aren’t sure what LEDs are good you may also read our post “The Best LEDs for Growing Weed”.

Choosing the Right Strains

There are a lot of strains that you can choose from to ensure quantity harvest. You have to select high-yielding strains. The following are some recommendations for high-yielding Cannabis strains:

  • Bruce Banner #3
  • Goldmine
  • Glookies
  • Holy Grail Kush
  • Malawi Gold or Chamba
  • Mimosa EVO
  • Monster Profit
  • Pure Kush
  • Super Critical Bud CBD
  • Wonder Woman

Training the Cannabis Correctly

Make your Cannabis grow relatively big during the vegetative stage before switching to a 12/12 photoperiod. When your plant is bigger, it can support larger buds. It would be best to wait before your Cannabis plant is half the length of your intended height before making it to the flowering stage.

Aside from that, you need to know how to train your Cannabis plants. This process will help you regulate the size of the branches of your plant and control where they will grow. You have to ensure that the canopy of your Cannabis can fill the entire light given by your grow lamps so you will not waste light. Take this instance that you are using a 600 watts HPS. It can approximately cover 4 feet by 4 feet growing area; thus, you need to ensure that your Cannabis plants’ canopy can cover every inch of your growing space.

You can make this happen by either growing the number of Cannabis plants in your space or simply training your Cannabis plants to grow flat and wide. To make the branches grow horizontally, all you need to do is tie them slightly tighter than you usually do.

Other Things to Remember

Before Switching Flowering Stage

  1. You need to clear the bottom 10% to 20% of your Cannabis plants since buds in that portion are in shadow and will only take away energy from the top buds that are more exposed under the light.
  2. Defoliate the biggest fan leaves of your Cannabis plants before or within the first week after switching to the flowering stage. Defoliation helps to get more light to the bottom of your cannabis plants.

Flowering Stage (after switching to 12/12)

  1. The light must remain steadfast and close to your crops without causing a light burn. So, you need to check the actual color of their leaves in natural light to ensure that leaves are not burned. You may review our article "How to Spot Light Burn in Cannabis Plants?"
  2. Defoliate the biggest fan leaves around week 3 to 4 after switching to 12/12. It will make light exposure more even to your entire crops and will help buds fatten up.

How to space grow lights for maximum efficiency when growing Cannabis?

Lighting is a critical factor in growing Cannabis indoors. In this matter, it will also ensure healthy crops and maximum yield in the end. You have to know how to position growing light at a certain distance from your Cannabis plants to avoid problems such as a light burn. The following are the recommended distance to growing light in different stages of your Cannabis:

Seedling Stage

Seedlings need less light so avoid exposing them to too much light intensity. It is safe to position your grow light between 24 inches to 36 inches (60 cm – 91 cm) from the top of the soil.

Vegetative Stage

It needs more intense light during this period since they need to develop strong and healthy roots and stems. This time, the light is recommended to be hanging closer to their canopy. It would be best to keep them between 12 inches to 24 inches (30 cm – 60 cm) from the top foliage of your Cannabis plants.

As a precautionary measure, you need to monitor them closely to see if they are getting enough or too much light. You may test it by placing your hands over the canopy and feeling the light intensity. If it is too hot for your skin, it would be the same for your plants.

Vegetative Stage

It would be best to position your light between 16 inches to 36 inches (41 cm – 91 cm) above the canopy during the final stage of the growth of your Cannabis. It is also advised to increase the distance gradually during the transition period from the vegetative to the flowering stage.

Does supplementing with CO2 increase cannabis growing efficiency?

Plants use Carbon Dioxide (CO2) for breathing when they manufacture energy from light through photosynthesis. The good thing is that fresh air naturally contains more than enough CO2 that helps plants keep growing and alive. Your Cannabis, in the same matter, needs CO2 to make energy; otherwise, they will starve and die.

When you supply extra CO2 in the air, your Cannabis plants utilize more light than they use. It increases energy manufactured by the plants beyond what is intended with your grow light, without fear of risk from a light burn. Thus, the extra energy will help your crops grow faster and enhance the quality of yields.

Aside from that, other known benefits of supplementing CO2 into your Cannabis are the following:

  1. When your growing environment is rich with CO2, your plants can stand higher temperatures. A growing space with 1,200 to 1,500 PPM of CO2 in the air can make your Cannabis withstand up to 95° Fahrenheit (30° Celsius). Thus, if you have a lot of hot and bright lights, it is best to supplement CO2 in your space.
  2. If you want to keep your cultivation of Cannabis a secret or you want security from people’s attention, CO2 can help you with that. Carbon Dioxide can prevent venting out hot or smelly air. Thus, it will cover up the odor of your Cannabis.
  3. Adding CO2 with HPS grow light can help the growth rate of your Cannabis plants by 20%. Also, LEC benefits from extra CO2. Big LEDs only get a moderate growth increase from additional CO2, especially in a hot growth area. In contrast, small LED benefits the least from a CO2-rich environment.

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